Help require to delete or reduce extra marks

Hi,

The rules changes time to time as per education policy structure of grace marks. So I want to delete the extra grace marks or reduce the extra grace marks >10 to 10 as per the second condition.

A student will get maximum 10 grace marks in a single subject. In short if the student has 23 marks then he will not get 12 grace marks but he will get only 10 grace marks. He will not pass in that particular subject. In this case after giving grace marks if the student is not reaching the passing marks that is 35 and 18 then no need to give grace marks; though the total of grace marks is not 15.
Secondly, the student will get grace marks maximum in only 4 subjects. These 4 subjects should be the highest. If the student has 6 subjects in which he is eligible of grace marks then the top 4 subjects get grace marks limit to 15.

Please suggest me a code to achieve the target automatically.

Thanking you.